The Iraqi assault on Iran is an almost perfect window on how things happen in that corner of the world -- as distinct from the way a lot of Americans, wistful for easier times, think the United States can still make things happen.

Former defense secretary James Schlesinger, for instance, sees the Iraqi-Iranian conflict in terms of a general "ebbing of U.S. power and influence." What's needed, he says, is "more U.S. military presence in the area" -- a large naval force and at least a division of U.S. Marines as an offset, somehow, for the 27 Soviet divisions he says are massed just north of the Russian-Iranian border.

What Schlesinger and others don't seem quite ready to accept, however, is that the shah is gone. Iran no longer has the strong central authority or the armed might that made it one of the "twin pillars" (with Saudi Arabia) of U.S. policy in the Persian Gulf and, in the process blood feud with Iraq whose roots are centuries old.

One can argue that all this might hve been avoided by a much earlier, more impressive show of American military force in support of the shah, as Schlesinger energetically recommended at the time. But that's not the same thing as saying that American gunboat diplomacy can still be counted on to influence the course of a conflict that is, at bottom, no more than the logical consequence of a power vacuum created by the revolutionary upheaval in Iran.

What we are witnessing, experts here contend, is Iraq's predictable bid, born of its own sense of destiny, for predominance in the Arab world. That's not to say that East and West have no geopolitical stake in the outcome. There's the irony: The united States and the Soviet Union have provided the hardware for a costly and potentially disastrous home-grown conflict whose outcome they are largely powerless to control.

True, the Soviets' profession of hands-off "neutrality" may be entirely for effect. But they don't sound comfortable. Their role as Iraq's arms supplier has not won them exceptional good will -- not in Iran, naturally, but not even in Iraq. The violence-prone government of Iraqi strongman Saddam Hussein has killed off local communists, resisted Moscow's control and given the Soviet military presence in the region as it is opposed to that of the Western "imperialists."

As for the Carter administration's prim preaching of "neutrality," that can hardly be an entirely comfortable position in the face of what would appear to be a clear case of Iraqi aggression, by the standards of the United States has traditionally applied.

But the administration is in a genuine bind. Any condemnation of Iraq for unjustified resort to force would inevitably be read as a certain sympathy for the Iranian side of the argument. That's hard to express, politically, while the hostages remain in captivity.

While Iranian authorities are proclaiming the Iraqi attack to be "part of a large U.S. plot" that will have its impact "on the destiny of the hostages," a claim of neutrality, on the other hand, can only fuel Iranian paranoia.

Some American experts insist Iranian suspicions are not only real but may even have been encouraged, intentionally or not. Administration critics are already beginning to mutter out loud about what seemed to them to have been calculated overtures to the Iraqis by national security adviser Zibqniew Brzezinski in a May interview on the PBS "MacNeil/Nehrer Report."

While specifically denying any intention of promoting Iraqi hostilities against Iran, Brzezinski said, "We see no fundamental incompatibility of interests between the United States and Iraq. We feel that Iraq desires to be independent, that Iraq wishes a secure Persian Gulf, and we do not feel that American-Iraq relations need to be frozen in antagonism."

But experts here are not nearly so relaxed now about Iraqi aims. The guessing is that Iraq war objectives are limited: to capture disputed territory for bargaining purposes; to humiliate Iran by way of building its own image as Arab leader, at the expense of Egypt's Anwar Sadat; and more ominously, to establish a precedent for whatever future designs Iraq might have on another, far more important slice of disputed territory -- Kuwait.

The test, then, is not one of America's "power and influence," but of Iraq's. To see it otherwise -- grandly, in global power-balancing terms, or narrowly, in terms of the effect on the hostages -- is to miss what experts here see as the real significance of the Iraqi-Iranian war.